DE10017256B4 - Process for the production of organic acids by means of high-performance continuous fermentation - Google Patents

Abstract

The present invention provides a process for the production of organic acids by high performance fermentation comprising the following steps: DOLLAR A continuous cultivation of bacteria producing organic acids and the recovery of organic acids produced in the culture using a cell-recycling, multi-stage, continuous fermentation plant with serially connected fermenters, each of which comprises a fermenter containing a fermentor vat, temperature control, stirrer and pH control; with pumps for the outflow circulation of the medium from the fermenter; and with cell separators for separating and circulating the media with the pumps. According to the present process, high concentrated lactic acid of 90 g / l can be produced with the high productivity of 50 g / l / h, which reduces the equipment cost and the production cost in the mass production process. In addition, the present invention can be effectively applied to the preparation of other organic acids such as acetic, formic, citric, malic, maleic, fumaric and succinic acid, which exhibit end-product inhibition.

Description

object the invention

The The present invention relates to a process for the production of organic acids with a high-performance fermentation, in particular a method for the production of organic acids in a high performance Way by cultivating organic acids producing Bacteria in a cell-recycling, multilevel, continuous Fermenter system.

background the invention

Organic acids such as lactic acid, acetic acid and citric acid, which are widely used in industry, have hitherto been produced by chemical synthesis, by enzymatic reactions or by microbiological fermentation processes. However, the cost-benefit problem has limited the availability of manufacturing processes other than chemical synthesis and many efforts have been made to replace the chemical process with more environmentally friendly fermentation processes. The importance of new methods has been recognized by the discovery of microorganisms capable of producing organic acids through the development of high-performance fermentation processes and the spread of environmental knowledge. Although fermentation technology is commonly employed in the acetic acid and citric acid production process, the practical utility of relatively low yield fermentation processes has been limited or sometimes completely prevented for other organic acids (see: Roehr, M., Products of Primary Metabolism in: Biotechnology, 2 ^nd Edition, Vol 6 (Rehm, H, J, Reed, G., Eds.). Weinheim:. Verlag Chemie, 1996).

Of course, were many approaches to establish a fermentation process for very important organic acids like lactic acid carried out, their physical properties and fermentation conditions and the results of lactic acid production by fermentation were transferred to the production of other organic acids. In the course of these activities was the lactic acid fermentation below Use of course occurring substances, e.g. Strength, Glucose, sugar and lactose, always increased and high performance fermentation processes should meet the enormous potential demand while chemical synthesis the lactic acid gradually decreased.

Lactic acids that are produced in the metabolism of living organisms in a variety of fermented foods, e.g. Kimchi (a traditional Korean fermentation product) and Yakult, contain. lactic acid has been since its first identification by Scheele in 1780 mainly in the US and in European countries produced. Lactic acid, which is optically active due to a chiral carbon atom, is in L and D-lactic acid classified, whereby humans are only able to the L-form too use. lactic acid is made by fermentation of microbes in the form of L- or D-lactic acid or depending on of specificity the enzymes of the microorganism sometimes as a racemate mixture of the two Molds made.

There the world market re lactic acid in the field of food and cosmetics in some ways is limited, there is a new need for the biodegradable Polymers and various solvents emerged quickly. To meet the needs to meet in the state of the art, It is essential to compare lactic acid with one usual Process to produce new high-efficiency process. biopolymers based on lactic acid can be easily degraded under environmental conditions and have regard to the mechanical stability good properties, indicating the use of lactic acid as the basic material for the Polymer synthesis makes it suitable.

To now became lactic acid produced using a batch fermentation process, the cultivation of lactic acid bacteria for more than 60 hours after inoculation and isolation of lactic acid the culture medium. The batch process has the advantage that the production of lactic acid in a high concentration of> 120 g / l, although a critical disadvantage of a lower volumetric productivity of <5 g / l / h Has. To compensate for this low productivity, that became Fermentation volume increases what again the cost of the production of fermentation equipment and the maintenance of the Facilities increased Has.

In an alternative approach, the prior art has proposed the cell recycling method, wherein the microorganisms in the fermenter are concentrated to increase productivity to overcome the low productivity of the batch fermentation process. This method employs the principle that the concentration of the enzyme for lactic acid production increases with the cell density in the fermenter, the method comprising the steps of: keeping the lactic acid bacteria in the fermenter using isolation techniques such as centrifugation and membrane separation; Culturing the lactic acid bacteria in a medium containing sugar as a main component; and recovering the culture containing lactic acid.

The Cell recycling method using the membrane separation was Researched in the US since 1980 and 1987, Cheryan et al. reported that one volumetric lactic acid productivity of 84 g / L / h and a lactic acid concentration of 117 g / l can be realized (see: Mehaia, M.A. and M. Cheryan, Process Biochemistry, Dec. 185-188, 1987). Cheryan et al. also have one volumetric lactic acid productivity of 22 g / L / h and a lactic acid concentration of 89 g / l (see: Tejayadi, S. and M. Cheryan, Appl. Microbiol. Biotechnol., 43: 242-248, 1995). The method according to the state However, the technique has proved to be less than satisfactory the results under normal conditions for continuous fermentation are not reproducible (see: Timmer, J. M. and J. Kromkamp, FEMS Microbiology Reviews, 14: 29-38, 1994). A productivity of 22 g / l / h and a concentration of 89 g / l lactic acid fermentation solution apply therefore as the highest Performance and concentration among the results of Cheryan from the Years 1995.

Although many results published obtained using the cell recycling process in one continuous fermentation of lactic acid were distinguished the result of Cheryan et al. over others by a high Concentration of> 90 g / l lactic acid in the fermentation solution. The difficulty in obtaining high levels of lactic acid is due to which causes strong end-product inhibition at a lactic acid concentration of> 50 g / l.

On the other side were multi-stage continuous fermentation processes developed to end product inhibition in the course of lactic acid fermentation mitigate, in which the steps of cultivating the microorganisms and the production of lactic acid be separated in order to obtain high productivity: this means that under Use of a multistage, continuous fermenter plant with two or more serially connected fermenters the bacterial growth was facilitated in the first fermenter, which contains a relatively low concentration of the final product to the Rate of lactic acid production to maintain these microorganisms. The final product is produced in the following fermenters to the desired high To get concentration.

Actually became from the multi-stage, continuous fermentation reports which Includes 2 or 10 stages, that she a highly efficient production of ethanol is allowed which one typical product whose production process is the end product inhibition shows. This could be due to other processes, such as the manufacture of lactic acid, monoclonal antibodies, Enzymes and drug fluids (See: Gooijer, C.D., et al., Enzyme-Microb. Technol., 18: 202-219, 1996). Based on the idea of the End product inhibition in the production of lactic acid, which shows the same appearance as in ethanol production, have Mulligan et al. two- and three-stage, continuous fermentation and conducted improved productivity of lactic acid production by 25% and 57%, respectively, compared to the one-step process. The productivity of Mulligan et al method, however, was due to the low cell concentration from 2 to 3 g / l relatively low (e.g., 3 to 5 g / l / h) (see: Mulligan, C.N., and B.F. Safi, Biotechnol. Bioeng., 38: 1173, 1991).

Under these circumstances Many attempts have been made to produce lactic acid with a high efficiency Method combining the cell recycling method and the multistage, continuous fermentation process carried out. When Problem has been found, however, that the production efficiency compared with chemical synthesis and batch fermentation can not be further improved: Accordingly, in the prior art Process for the production of lactic acid energetically explored with high concentration and with high efficiency, because the highly efficient production of lactic acid to other organic acids, such like acetic acid, formic acid, Citric acid, malic acid, maleic acid, fumaric acid and succinic acid can be applied.

Nabisco Brands Inc. used serially connected two-stage fermenters to increase the final concentration of acetic acid and membranes between the two fermentors to concentrate the microorganisms in each fermentor (see: US Patent No. 4,456,622). However, it has been found that the fermenter is a single fermenter, two being by the batch process working fermenters were connected together, simply to reuse the microorganisms after fermentation. Accordingly, acetic acid can not be produced with high concentration and productivity as compared with the chemical synthesis.

Therefore existed continually a need to develop a new process for the production of lactic acid highly efficient way of producing others organic acids can be applied.

The DE 42 12 187 C1 discloses a process for continuous acetic acid fermentation with two fermenters wherein the contents of the first fermenter are transferred to the second and the second fermenter is subjected to residual fermentation, both fermenters being connected in series. In the DE 42 12 187 the dilution rate for the fermenter 2 is less than 0.12 h ^-1 . The dilution rate of the fermenter 1 is 0.165 h ^-1 . The dilution rates for Reactor 1 and 2 given in Examples 2 to 4 are in no case more than 0.165 h ^-1 . It follows that the total dilution rate is very low.

adversely That is why productivity is of the described fermentation process for organic acids low is. The technical task was therefore productivity of fermentation process for organic acids to increase.

Summary the invention

The Inventors have attempted an improved method of manufacture of highly concentrated lactic acid with the help of a highly efficient fermentation by a cell-recycling, multi-stage, continuous fermenter plant applied with two-stage serially connected fermenters will and have found that the lactic acid with a high concentration of> 90 g / l and a productivity of> 50 g / l / h can be. This method can be effective on other fermentation methods for the production of organic acids, which also show the end product inhibition can be applied.

A The first object of the present invention is therefore a method for the production of organic acids in a high concentration and with high productivity.

The Another object of the invention is to provide a cell-recycling, multi-stage, continuous fermenter system with serially connected fermenters provide.

The technical problem has been solved by a process for producing organic acids by cell-recycling, multi-stage, continuous fermentation comprising the steps of culturing bacteria producing organic acids in a fermentation medium and recovering the organic acids produced in the culture using a fermenter with serially connected, continuously operated fermentors, each of these fermenters comprising a fermentor vat, temperature control, stirrer, pH control; with pumps for the outflow circulation of the media from the fermenters; and with cell separators for separating and circulating the media with the pumps, wherein the separated cells are fed back into the fermenters, and wherein the serial connection of the fermenters is that the fermentation solution is fed together with filtered fermentation solution under control of the inflow into the second fermenter wherein the continuous cultivation is carried out at a dilution rate (final flow rate / total fermentation volume) of 0.3 to 0.7 hr ^-1 and a withdrawal ratio (withdrawal rate / dilution rate) of 0.01 to 0.1.

Short description the drawings

The above and the other objects and features of the present invention are described more graphically by the following description, given in conjunction with the attached drawings, in which:

1 Figure 3 is a schematic diagram illustratively describing the structure of the cell recycling, two-stage, continuous fermentor plant of the present invention.

2 Figure 3 is a schematic diagram illustratively describing the cell separator and pump assembly in the cell-recycling, two-stage, continuous fermentor system.

3 is a graph showing the properties of the batch fermentation of lactic acid.

4 Figure 4 is a graph showing the properties and productivity of lactic acid fermentation in a cell-recycling, two-stage, continuous fermentor plant.

detailed Description of the invention

One Process for the production of organic acids by means of highly efficient Fermentation according to the present Invention the steps: continuous cultivation of bacteria producing organic acids and recovery of the organic acids produced in the culture, application a cell recycling, multi-stage, continuous fermenter plant with a cell recycling device and serially connected Fermenters.

The Cell-recycling device includes cell separators and pumps, wherein the cell separators include centrifuges or membrane separators, in particular prefers membrane separators to microorganisms from the growth medium and to separate from the fermentation product. Among the reverse osmosis membranes, Ultrafiltration membranes and microfiltration membranes are ultrafiltration membranes due to the disadvantages of other membranes the most suitable means for cell separation: reverse osmosis membranes have a relatively low Filtration capacity. The microfiltration has the disadvantage despite its high filtration capacity a quick decline the efficiency due to the clogging with microorganisms from the fermentation solution and / or Media components. To the high filtration capacity of microfiltration To maintain two filters are alternately kept in operation and while The operation of the one filter should be the traces or residues in the other filters are washed out. The ultrafiltration membrane despite its low filtration capacity has the advantage of a longer operating time to allow.

There the feeder of the medium, the removal of the fermentation solution, the cell separation and cell recycling in the cell recycling device of the invention At the same time, flux control pumps are needed, such such as peristaltic pumps, diaphragm pumps, gear pumps or combined devices the same. The pumps are before and after the continuous fermenters and cell separators arranged or between the continuous Fermenters and cell separators. The function of the pumps is to to lead the medium into the fermenter, the fermentation solution outside to circulate the fermenter or the fermentation solution to be removed from the fermenter.

The continuous fermenter can be connected to 2 to 6 stages, depending on the characteristics of the final product.

Everyone the serially connected fermenter comprises a fermenter vat, Temperature control, stirrer, pH control and optionally a gas injector (if a gas for the Growth of the microorganism or for the formation of the product needed becomes). In the case of lactic acid bacteria it is not due to the anaerobic conditions of cultivation necessary, additional To initiate gas. However, nitrogen gas could be injected into the fermenter to complete anaerobic conditions guarantee, the most critical for other bacteria could be the other organic acids produce. Furthermore could acids or alkalis in the form of a solution or a gas introduced into the fermenter to adjust the pH the fermentation solution to control.

to The serial connection of the cell-recycling fermenter becomes the filtered one fermentation solution from the cell recycling device to the second fermenter supplied under control of the inflow, and the removal, with the microorganisms are removed from the fermentation solution, in the second fermenter fed under control of the inflow to the continuous high concentration fermentation upright receive. The fermentation solution is also recycled or discharged into the second fermenter below Use the cell-recycling device to the most efficient Production of highly concentrated organic acid to realize. During the Cell-recycling, multistage, continuous fermentation become the organic acid forming bacteria by the continuous recycling of microorganisms held in high concentration with the cell separator in the fermenter. The fermentation broth exists Sugars, such as glucose, lactose, sucrose or starch Main components from the outside to the fermentation solution added can be. The optimal conditions for the fermentation of organic acids can be maintained, by increasing the cell concentration is prevented by means of pumps, the Remove small amounts of the microorganism-containing fermentation solution. In this case, the reduction of the fermentation capacity by means of pumps to remove microorganism-free fermentation solution after outside be prevented.

The Method according to the present invention Invention will be described in the following description of cell-recycling, multi-stage, continuous fermenter plant and its operation shown.

1. Cell-recycling, multistage, continuous fermenter plant

A cell recycling apparatus equipped with a cell separator and pumps is used to increase the concentration of microorganisms in a continuous fermenter. The microorganisms are separated and returned to the fermenter, while the fermentation solution containing the produced lactic acid and remaining components of the medium is filtered and fed to the second continuous fermenter. In operating the multi-stage, continuous fermentation, the microorganisms are gradually concentrated, although the performance of the pumps and the cell separator is reduced. Therefore, the fermentation solution should be withdrawn at a constant rate and added to the second fermenter along with the filtered fermentation solution. By this extraction, the concentration of the microorganisms increases to a high level and reaches the equilibrium, and the cultivation can gradually proceed in the second continuous fermenter, the cell concentration being continuously maintained by the filtration apparatus having the same function as in the previous stage (please refer: 1 ). In 1 represents (m) the externally introduced medium; (ri1) and (ro1), cell recycling in the first stage; (b1) removal in the first stage; (p1) the path of the filtrate in the first stage; (ri2) and (red) cell recycling in the second stage; (b2) removal in the second stage; and (p2) the path of the filtrate in the second stage. Like in the 1 For example, more than two stages of fermentors may be serially connected to a cell-recycling, multi-stage, continuous fermentor unit, each equipped with a cell separator to filter the fermentation solution and pumped to remove the microorganism-containing fermentation solution (b1 and b2) to maintain the high level of cell concentration. Pumps also play a role in the introduction of the medium (m), in cell recycling (ri1 and ri2) and in filtrate flow control (p1 and p2) (see: 2 ). The basic conditions of the fermentation, such as temperature and pH, are controlled with a controller installed in each continuous fermenter. To control the pH, pumps for the addition of ammonia may be provided in the fermentor.

Around the organic acid continuously and steadily using the cell recycler, multistage, continuous fermenter plant should produce the long-term operation with constant fermentation volume, consistent Concentration of microorganisms and constant fermentation substrate, be maintained to balance the continuous fermentation to reach.

2nd operation

As previously described fully, the operating factors that are critical at each fermentation stage in the cell-recycling, multi-stage, continuous fermentation include fermentation volume, medium flow rate, and microorganism removal rate. The appropriate ranges for these factors can be optimized from the simulation study, though they should be verified by real experiments. The highest productivity of highly concentrated organic acids can be achieved with the smallest fermentation volume under optimized conditions. In this regard, the inventors carried out the cell recycling continuous fermentation with the serially connected, two-stage, continuous fermentor plant along with the simulation study. In the two-stage continuous fermenter system, the fermentation volume ratio, the flow rate of the medium and the rate of withdrawal of the microorganisms were controlled by the ratio of the dilution rate (D, final flow rate / total fermentation volume) and the withdrawal ratio (withdrawal rate / dilution rate). As a result, it was determined that the optimized conditions for the lactic acid production with a high concentration and high productivity are as follows: the dilution rate of 0.3 to 0.7 h ^-1 , the withdrawal ratio of 0.01 to 0.1 in each stage and the fermentation volume rate of 10: 1 to 0.3: 1.

The serial connection to the two-stage continuous fermenter system increased the productivity of lactic acid by 100% or more, compared to the results of Cheryan et al. from 1995, indicating that the present method with respect to its efficiency across from the single-stage continuous fermentation, compared to the batch fermentation or chemical synthesis was improved. additionally can through the highly efficient production of other organic acids Application of cell recycling, multistage, continuous Fermenter plant on the production of other organic acids, which also show an end product inhibition, such as acetic acid, formic acid, citric acid, malic acid, maleic acid, fumaric acid or succinic acid, will be realized.

The the present invention is further illustrated in the following examples, which are not intended to limit the scope of the invention. In particular For example, the process for producing organic acids by high performance fermentation according to the present Invention not only on the lactic acid, as in the examples shown to be applied, but also to other organic acids, which show the end product inhibition. Accordingly, the present covers Invention all processes for the production of organic acids, including lactic acid, by Application of cells-recycling, multistage, continuous Fermenter from.

Example 1: batchwise fermentation

; ausgefülltes Dreieck, Spitze nach oben) die Zellkonzentration als Trockengewicht; (

; offener Kreis) die Glukosekonzentration; und (

; offenes Rechteck) die Milchsäurekonzentration. Wie in der 3 gezeigt, wurde die höchste Milchsäurekonzentration von 112 g/l nach 60 Stunden bei der chargenweisen Fermentation erreicht, während die volumetrische Produktivität bei 2,3 g/l/h lag.Batch fermentation was performed to examine the productivity and concentration of lactic acid using the lactic acid bacteria Lactobacillus rhamnosus (ATCC 108863): 1 ml aliquots of L. rhamnous sus in glycerol-containing MRS (Difco, USA) at -70 ° C stored for later use as seed germ. The media for the batch fermentation contain 150 g / l glucose, 15 g / l yeast extract (Difco, USA) 2.5 g / l KH ₂ PO ₄ , 0.5 g / l Na ₃ citrate 2H ₂ O, 0 , 2 g / l MgSO ₄ .7H ₂ O, 0.03 g / l MnSO ₄ .H ₂ O, 0.03 g / l FeSO ₄ .7H ₂ O, 0.03 g / l ZnSO ₄ .7H ₂ O and 0.015 ml / l H ₂ SO ₄ . 100 ml MRS medium was inoculated with seed germs, cultured for 12 hours with shaking, and the culture medium transferred to a 2 liter fermentor. Thereafter, ammonia gas was added to the fermentation medium to neutralize the lactic acid produced during the fermentation and to reach a pH of 6.0. The fermentation was carried out at a uniform temperature of 42 ° C. The cell concentration in the fermentation broth was obtained by the reciprocal of the OD at 620 nm measured in the spectrophotometer (Ultraspec-300, Pharmacia, England) after dilution of the fermentation solution. The glucose and lactic acid concentrations in the fermentation solution were measured by HPLC with an RI detector after the fermentation solution was centrifuged and the microorganisms were removed using Aminex HPX-87H (Biorad, USA) as HPLC column and 10 μl of 10 μl. diluted dilution fermentation solution was injected. The cell, glucose and lactic acid concentrations during the fermentation process were determined for 60 hours by the method described above (see: 3 ). In 3 represents (

; solid triangle, top to top) the cell concentration as dry weight; (

; open circle) the glucose concentration; and (

; open rectangle) the lactic acid concentration. Like in the 3 The highest lactic acid concentration of 112 g / l was achieved after 60 hours in the batch fermentation, while the volumetric productivity was 2.3 g / l / h.

Example 2: Cell Recycling, single-stage, continuous fermentation

The cell-recycling, single-stage, continuous fermentation was carried out with a fermentation volume of 250 ml using a hollow fiber ultrafiltration membrane (UFP-500-C-4A, A / G Technology, USA) to improve the productivity and lactic acid concentration compared to those of the observed batchwise fermentation in Example 1. The fermentation was carried out under two conditions: 1) withdrawal ratio 0.042 and dilution rate 0.62 h ^-1 ; and 2) withdrawal ratio 0.078 and dilution rate 0.72 h ^-1 . The composition of the medium is shown in Table 1.

Table 1

When Result it could be determined that the cell concentration was 120 and 90 g DCW (dry cell weight) / l or that the Lactic acid productivity 33 or 38 g lactic acid / l / h amounted to. Although the values are higher were as those of batch fermentation, concentration was the lactic acid less than 50 g / l under the two experimental conditions, indicating that one significant improvement was not achieved. As is the activity of microorganisms for the production of lactic acid at the high lactic acid concentration decreased from 50 g / l, the lactic acid concentration, despite the high cell concentration of 120 g DCW / L can not be increased. From the above results it could be concluded that a low Level of dilution rate must be maintained or a cell-recycling, multistage, continuous fermentation introduced must become, to highly concentrated lactic acid manufacture.

Example 3: Cell Recycling, two-stage, continuous fermentation

; ausgefüllter Kreis) die Glukosekonzentration im ersten kontinuierlichen Fermenter; (

; offener Kreis) die Glukosekonzentration im zweiten kontinuierlichen Fermenter; (

; ausgefülltes Rechteck) die Zellkonzentration im ersten kontinuierlichen Fermenter; (☐; offenes Rechteck) die Zellkonzentration im zweiten kontinuierlichen Fermenter; (

;ausgefülltes Dreieck auf der Spitze stehend) die Milchsäurekonzentration im ersten kontinuierlichen Fermenter; (

; offenes Dreieck auf der Spitze stehend) die Milchsäurekonzentration im zweiten kontinuierlichen Fermenter; (

; offene Raute) die Verdünnungsrate in der Fermentation; (

; ausgefüllte Raute) die Produktivität. Wie in 4 gezeigt, wurde die Konzentration der Mikroorganismen im ersten Fermenter bei 100 gDCW/l aufrecht erhalten, während die Endkonzentration der Milchsäure über 90 g/l betrug und die Milchsäureproduktivität bei über 50 g/l/h lag. In diesem Fall betrug die verbleibende Glukosekonzentration weniger als 3 g/l, was anzeigt, daß die Glukose fast vollständig in Milchsäure umgewandelt wurde.The high productivity of the lactic acid fermentation was achieved by using the cell-recycling, multi-stage, continuous fermenter plant, which was higher in productivity than in the batch fermentation or cell-recycling single-stage fermentation: two continuous fermenters were connected in series; the cell concentration in each fermenter was maintained at over 100 g DCW / L; the lactic acid concentration in the first and second fermenters was maintained in the range of 40 to 60 g / l and above 90 g / l, respectively. The ultrafiltration membranes UFP-100H-6A (A / G Technology, USA) and Pellicon-2mini B-100V (Millipore Co., USA) were used and the fermentation solution volume in each fermentor was maintained at about 600 ml. The same media as in Example 2 was used except that 105 g / L of glucose and 13 g / L of yeast extract were continuously added. The withdrawal ratio was controlled in the range of 0.02 to 0.08 and the dilution rate of 0.5 h ^-1 to 0.6 h ^-1 . A duration of 45 hours for the fermentation was sufficient to achieve equilibrium conditions (see: 4 ). In 4 means (

; filled circle) the glucose concentration in the first continuous fermenter; (

; open circuit) the glucose concentration in the second continuous fermenter; (

; filled rectangle) the cell concentration in the first continuous fermenter; (□, open rectangle) the cell concentration in the second continuous fermenter; (

filled triangle on the tip) the lactic acid concentration in the first continuous fermenter; (

; open triangle on top) the lactic acid concentration in the second continuous fermenter; (

; open diamond) the dilution rate in the fermentation; (

; filled diamond) the productivity. As in 4 The concentration of microorganisms in the first fermenter was maintained at 100 gDCW / L while the final lactic acid concentration was above 90 g / L and the lactic acid productivity was above 50 g / L / hr. In this case, the remaining glucose concentration was less than 3 g / L, indicating that the glucose was almost completely converted to lactic acid.

As clearly illustrated and demonstrated above, the present invention provides a process for the production of lactic acid by high performance fermentation using a cell-recycling, multi-stage, continuous fermentor system with serially linked cell-recycling continuous small fermenters. According to the present process, high-concentration lactic acid of 90 g / l can be produced with the high productivity of 50 g / l / h, which is much higher than that achieved by conventional methods. In addition, the present invention can be applied to the preparation of other organic acids such as acetic, formic, citric, malic, maleic, fumaric, and succinic acids, which exhibit end-product inhibition.

It is for Professionals obvious that certain changes and modifications can be made in this invention without the spirit or scope of the invention as shown here was to leave.

Claims (4)

A process for producing organic acids by cell-recycling, multi-stage, continuous fermentation comprising the steps of cultivating organic acid-producing bacteria in a fermentation medium and recovering the organic acids produced in the culture using a fermenter with serially connected, continuously operated fermentors each of these fermenters comprising a digester vat, temperature control, stirrer, pH control; with pumps for the outflow circulation of the media from the fermenters; and with cell separators for separating and circulating the media with the pumps, wherein the separated cells are returned to the fermenters, and wherein the serial compound of the fermenters is that the fermentation solution is fed together with filtered fermentation solution under control of the inflow into the second fermenter characterized in that the continuous cultivation is carried out at a dilution rate (final flow rate / total fermentation volume) of 0.3 to 0.7 h ^-1 and a withdrawal ratio (withdrawal rate / dilution rate) of 0.01 to 0.1. Method according to claim 1, characterized in that that the Fermenter plant has 2 to 6 serially connected fermenters. Method according to claim 1, characterized in that the organic acid Lactic acid, Acetic acid, formic acid, Citric acid, malic acid, maleic acid, fumaric acid or Succinic acid is. Method according to claim 1, characterized in that that the continuous cultivation is carried out at a fermentation volume rate from 10: 1 to 0.3: 1.